Method for manufacturing an erect image, unity magnification, resin lens array

ABSTRACT

The present invention provides a method for manufacturing an erect image, unity magnification, resin lens array by injection molding. Two injection-molded lens plates are stacked such that convexly warped sides thereof face each other or such that a convexly warped side of the lens plate whose warp is greater than that of the other lens plate faces a concavely warped side of the other lens plate, while directions of resin injection thereof are aligned so as to optically avoid the influence of molding shrinkage. Engagement spigots and engagement sockets are employed in order to align the two lens plates. The two stacked lens plates are secured by clipping of peripheral portions thereof.

This application is a Divisional Application, claiming the benefit ofU.S. patent application Ser. No. 09/380,042, filed Aug. 25, 1999, nowU.S. Pat. No. 6,363,603, which is a U.S. National Phase Application ofPCT International Application PCT/JP98/05851 filed Dec. 24, 1998.

TECHNICAL FIELD

The present invention relates to an erect image, unity magnification,resin lens array and to a method for manufacturing the same. Moreparticularly, the invention relates to an erect image, unitymagnification, resin lens array applicable to a device for spatiallytransmitting a two-dimensional image and a method for manufacturing thelens array, as well as to a method for manufacturing a mold for use inmanufacture of the lens array.

BACKGROUND ART

An erect image, unity magnification lens array used in a copier,facsimile, or printer is disclosed in Japanese Patent ApplicationLaid-Open No. 55-90908. The publication proposes a two-block lens arrayin which each block includes a number of bar lenslets and the two blocksare arranged so as to face each other. Such a lens array is formed bythe steps of, for example, covering with an acrylic resin a lens supportin which through holes are bored at positions corresponding to intendedbar lenslets; and pressing dies having hemispherical concaves formedtherein against the acrylic resin assembly from the opposite side tothereby form end faces of bar lenslets.

Japanese Patent Application Laid-Open No. 64-88502 discloses a lensarray including two flat lenses which face each other. Each flat lens isformed by injection molding such that convex lenslets are arrayed in atwo-dimensional regular pattern.

FIG. 8 of Japanese Patent Application Laid-Open No. 60-29703 depicts ausually practiced method for manufacturing a microlens array. Accordingto the method, a polymer is deposited on a mold having concaves formedtherein in an array, thereby forming the microlens array.

Japanese Patent Application Laid-Open No. 5-150102 discloses a methodfor manufacturing a microlens array, comprising the steps of: forming amask layer on a flat plate; forming fine circular openings at intendedlenslet positions in the mask layer, in a number equal to the number ofintended lenslets; chemically etching the surface of the flat platethrough the openings; removing the mask layer; further chemicallyetching the surface of the flat plate to obtain a mother matrix;fabricating a mold for use in molding a microlens array, by use of themother matrix; and pressing a glass sheet against the mold (theso-called “2P molding process”), thereby fabricating a microlens arrayon which convex lenslets are densely formed on one side.

An ordinary resin lens array is intended to converge luminous flux oneach of arrayed targets. Accordingly, the accuracy of lenslet pitchesmust be equivalent to the positional accuracy of the targets. To thisend, the resin lens array must be manufactured by the 2P moldingprocess.

An erect image, unity magnification, resin lens array is applicable notonly to a copier, facsimile, or printer but also to a two-dimensionalimage, spatial transmitting device for transmitting a two-dimensionalimage onto a spatial image plane. A specific example of such atransmitting device is a touchless switch. An erect image, unitymagnification, resin lens array for use in such a two-dimensional image,spatial transmitting device is not required to have a high degree oflenslet pitch accuracy so long as the optical axes of at least threestacked hemispherical lenslets are aligned.

The inventors of the present invention carried out extensive studies inan attempt to manufacture an erect image, unity magnification, resinlens array by injection molding, not by a 2P molding process.

An erect image, unity magnification, resin lens array which the presentinventors aim to provide includes at least two lens plates, which eachhave hemispherical lenslets of 0.2 mm to 2.0 mm diameter arrayed in aregular pattern on one or both sides thereof. The lens plates arestacked such that the optical axes of at least three stackedhemispherical lenslets are aligned. The working distance of the intendedlens array is not greater than 100 mm. Accordingly, the stackedhemispherical lenslets of the lens plates have a common optical axis,and the common optical axes are in parallel to each other.

As mentioned previously, Japanese Patent Application Laid-Open No.64-88502 describes that a flat lens array is manufactured by injectionmolding, but the publication does not disclose a specific proceduretherefor. According to Japanese Patent Application Laid-Open No.5-150102, a Ni mold for use in fabrication of a microlens array ismanufactured. However, this Ni mold is not applicable to injectionmolding which the present inventors aim to provide. In the case where aglass mother matrix is fabricated, if a pinhole is present in a chromiumfilm, glass is etched through the pinhole, resulting in formation of anundesirable pit in the glass mother matrix. As a result, a moldfabricated by use of the glass mother matrix involves a defect.

Further, when a lens plate is manufactured by injection molding, theinjection-molded lens plate is warped and suffers molding shrinkage.Therefore, when the warped, shrunk lens plates are assembled into anerect image, unity magnification, resin lens array, there must bedevised a measure for rendering the lens array free of distortion.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method formanufacturing an erect image, unity magnification, resin lens array byinjection molding through use of a defect-free mold.

Another object of the present invention is to provide an erect image,unity magnification, resin lens array manufactured by the method of theinvention.

Still another object of the present invention is to provide a lens platefor use in the aforementioned erect image, unity magnification, resinlens array and a method for manufacturing the lens plate by injectionmolding.

A further object of the present invention is to provide a mold for usein the aforementioned injection molding and a method for manufacturingthe mold.

A still further object of the present invention is to provide a mothermatrix for use in manufacture of the aforementioned mold and a methodfor manufacturing the mother matrix.

A still further object of the present invention is to provide a mastermatrix for use in manufacture of the aforementioned mother matrix and amethod for manufacturing the master matrix.

The erect image, unity magnification, resin lens array of the presentinvention includes lens plates which each have hemispherical lensletsarrayed in a regular pattern. According to the method of the inventionfor manufacturing the resin lens array, first there is manufactured amaster matrix for a mold for use in injection-molding of the lens plate.The master matrix is manufactured by the steps of: preparing a glasssubstrate having substantially parallel, flat surfaces; forming anetching resist film on the glass substrate; patterning the etchingresist film so as to form fine openings corresponding to thehemispherical lenslets in the etching resist film in a regularly arrayedpattern; isotropically etching the glass substrate while using thepatterned etching resist film as a mask, thereby forming concaves in theglass substrate under the corresponding fine openings; removing thepatterned etching resist film; further isotropically etching the glasssubstrate so that the concaves grow and assume a profile correspondingto that of the hemispherical lenslet.

By use of the thus-manufactured master matrix, the mold for use ininjection molding is manufactured. A method for manufacturing the moldincludes the steps of: applying a parting agent onto the surface of themaster matrix on which the concaves are formed; drying the appliedparting agent; dropping resin onto the surface of the master matrix;spreading the dropped resin by use of a glass substrate; curing thespread resin; parting the master matrix from an assembly of the curedresin and the glass substrate; forming a conductive film on the surfaceof the cured resin of the assembly; depositing metal on the conductivefilm to a predetermined thickness by plating; and parting the resultantmetal plating from the assembly to thereby obtain the mold.

Next, a lens plate is manufactured by use of the thus-obtained molds. Amethod for manufacturing the lens plate includes the steps of: attachingtwo molds onto a die set such that surfaces having concaves formedtherein face each other; establishing a predetermined gap between thefacing molds; injecting resin into the gap; and opening the molds apartto remove the lens plate.

Subsequently, the thus-obtained lens plates are assembled into an erectimage, unity magnification, resin lens array. The assembling methodincludes the steps of: stacking two lens plates, which are convexlywarped, such that convexly warped sides thereof face each other or facein the same direction while directions of resin injection thereof arealigned; and clipping the lens plates together at clipping portionsthereof.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1H are views depicting the steps of a process forfabricating a glass master matrix;

FIGS. 2A and 2B are views illustrating the effect of a pinhole;

FIGS. 3A to 3E are views depicting the steps of a process forfabricating a mother matrix;

FIGS. 4A to 4C are views depicting the steps of a process forfabricating an Ni mold by use of the mother matrix;

FIG. 5 is a view depicting an Ni plating method;

FIGS. 6A and 6B are views depicting the steps of a process forfabricating a lens plate by injection molding through use of the Nimolds;

FIG. 7 is a plan view of a lens plate fabricated by injection molding;

FIGS. 8A and 8B are views illustrating arrays of lenslets;

FIGS. 9A and 9B are views illustrating a method of stacking lens plates;

FIG. 10 is an explanatory view illustrating molding shrinkage of thelens plate;

FIG. 11 is an explanatory view illustrating clearance between anengagement socket and engagement spigot;

FIGS. 12A to 12C are views depicting the steps of a procedure forassembling two lens plates into a lens array;

FIGS. 13A to 13C are views depicting the steps of a procedure forassembling two lens plates into a lens array while a colored plate issandwiched therebetween;

FIG. 14 is a view illustrating a spatial transmission of an imagethrough an erect image, unity magnification, resin lens array; and

FIG. 15 is a graph showing an MTF characteristic of the erect image,unity magnification, resin lens array of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will next be described in detailwith reference to the drawings.

FIGS. 1A to 1H depicts the steps of a procedure for fabricating a glassmaster matrix. The steps will be sequentially described below.

[1] Fabrication of Glass Master Matrix

(a) Preparation of Glass Substrate

As shown in FIG. 1A, a glass substrate 10 having polished, substantiallyparallel, flat surfaces is prepared. The glass substrate 10 may be of,for example, soda-lime glass or quartz glass. The present embodimentuses quartz glass. The reason for this is to avoid the followingproblem. If glass contains impurities and is etched in a hydrofluoricacid solution, which will be described later, the impurities in theglass will react with the solution to become fluorides. Thethus-produced fluorides, such as barium fluoride and boron fluoride,form precipitates, which hinder circulation of the solution and adhereto the glass surface with a resultant failure to form lenslets ofuniform hemispherical surface.

The thickness of the glass substrate 10 is preferably not less than 1.0mm. The employment of the thickness range prevents breakage of the glasssubstrate during a later step for parting the glass substrate from aresin body, which breakage might occur due to a reduction in thethickness of the glass substrate caused by etching even though the backsurface of the glass substrate is coated with a film resistant to anetchant (hereinafter referred to as an “etching resist film”).

(b) Formation of First Etching Resist Film

Next, as shown in FIG. 1B, a chrome film (a multilayer film of chromiumor chromium oxide) 12, which serves as a first etching resist film, isformed on the upper surface of the quarts glass substrate 10. Thethickness of the chrome film 12 is preferably 100 to 5000 angstroms. Theemployment of the thickness range reduces the possibility of formationof a pinhole in the chrome film 12 caused by remaining abrasive,adhering dust or dirt, or a projection on the glass surface and preventscracking of the chrome film 12 which might otherwise be induced by afilm stress.

(c) Patterning of the Chrome Film

Next, as shown in FIG. 1C, a photoresist 14 is applied onto the chromefilm 12 to a thickness of about 2 μm and is then exposed to lightthrough a photomask (not shown), followed by development to obtain apatterning resist. Subsequently, the chrome film 12 undergoes reactiveion etching so as to be patterned. Specifically, circular openings of a3 to 20 μm diameter or polygonal openings of a 3 to 20 μm maximumdiameter are formed through the chrome film 12.

The photoresist 14 used for patterning the chrome film 12 is removed,but may be left on the chrome film 12 so as to serve as a second etchingresist film. When the photoresist 14 is removed and the glass substrate10 is etched through the patterned chrome film 12, a pinhole, if any, inthe chrome film 12 will cause formation of an undesirable concave in theglass substrate 10. If the photoresist 14 is left unremoved, the pinholeis covered with the photoresist 14, so that such an undesirable concaveis not formed in the glass substrate 10.

In order to reduce the possibility of formation of a pinhole in thechrome film 12 caused by a pinhole in the photoresist 14, the followingsteps (d) and (e) may be added.

(d) Application of Photoresist onto the Second Etching Resist Film

As shown in FIG. 1D, photoresist (positive type) 16 is applied onto thesecond etching resist film (photoresist) 14 to a thickness of about 2μm.

(e) Patterning of the Photoresist through Exposure Effected from behindPatterned Chrome Film

Next, as shown in FIG. 1E, the photoresist 16 is exposed to lightemitted from behind the patterned chrome film 12, which serves as aphotomask. If a pinhole (≦1 μm) is formed in the photoresist 14, anassociated pinhole is also formed in the chrome film 12 in step (c). Thephotoresist 16 is exposed to light emitted from behind the chrome film12 through the pinhole formed in the chrome film 12. However, thediameter of the pinhole is too small to allow an exposed region toexpand up to the upper surface of the photoresist 16.

This condition is depicted in FIGS. 2A and 2B. FIG. 2A shows an exposedregion 18 in the photoresist 16 when the photoresist 16 is exposed toultraviolet rays emitted from behind the chrome film 12 through anintended opening of the pattern. The exposed region 18 expands up to theupper surface of the photoresist 16.

FIG. 2B shows an exposed region 22 in the photoresist 16 in the casewhere a pinhole is formed in the chrome film 12 due to a pinhole 20present in the photoresist 14 and the photoresist 16 is exposed toultraviolet rays emitted from behind the chrome film 12 through thepinhole. The exposed region 22 does not reach the upper surface of thephotoresist 16.

After the exposure to ultraviolet rays, the photoresist 16 undergoesdevelopment. A portion of the photoresist 16 corresponding to theexposed region 18 is removed; however, a portion of the photoresist 16located above the pinhole 20 is not removed. Accordingly, thephotoresist 16 of FIG. 1E is patterned to a desired pattern. Therefore,the thus-patterned photoresist 16 serves as a third etching resist filmwhich prevents the glass substrate 10 from otherwise being etched to apattern other than a required pattern in the next step.

Alternatively, after the photoresist 14 formed in step (c) is removed,steps similar to steps (d) and (e) may be added so as to form a secondetching resist film.

(f) First Glass Etching

Next, the glass substrate 10 coated with the etching resist films 12,14, and 16 are immersed in a hydrofluoric acid solution, which serves asan etchant, and undergoes isotropic etching which is effected by theetchant introduced through openings formed in the etching resist films12, 14, and 16. As a result, as shown in FIG. 1F, concaves 17 are formedin the glass substrate 10.

When the glass substrate 10 was etched for about 80 minutes while thediameter of the opening in the etching resist films 12, 14, and 16 wasabout 5 μm, the diameter of the formed concave was 153 μm.

(g) Removal of the Etching Resist Films

Next, as shown in FIG. 1G, the etching resist films 12, 14, and 16 areremoved.

(h) Second Glass Etching

Next, as shown in FIG. 1H, the glass substrate 10 in which the concavesare formed is immersed in a hydrofluoric acid solution and furtherundergoes isotropic etching. When the glass substrate 10 having theconcaves of a 150 μm diameter formed therein underwent isotropic etchingfor about 420 minutes, the concaves were grown to each have a diameterof 600 μm and a depth of about 74 μm.

In this case, in order to prevent a reduction in the thickness of theglass substrate 10, an etching resist film, such as a photoresist ormetallic film, may be formed on the back surface of the glass substrate10 opposite the surface on which the concaves are formed.

In the above-described process for fabricating the glass master matrix,fine openings are formed in the chrome film by reactive ion etching.However, a method for forming the fine openings is not limited thereto.The chrome film may be irradiated with a laser beam, which is anelectromagnetic wave, so that fine openings are formed therein throughapplication of heat and evaporation.

A laser beam is a parallel pencil of rays of uniform phase and ismonochromatic radiation. Because of such characteristics of a laserbeam, a laser beam converged through a lens produces a high energydensity. The wavelengths of emission lines range from about 2300angstroms, which is a wavelength of ultraviolet rays, to 0.7 mm, whichis a wavelength of sub-millimeter waves, and at least 500 differentemission lines exist.

A substance has an energy (wavelength) absorption band. By selecting alaser beam whose wavelength falls within the wavelength absorption bandof a certain substance, the substance can be heated (as in the case of,for example, a laser marker or laser knife). Through utilization of thefact that the chrome film and the glass substrate are different inwavelength absorption band, fine openings can be formed in the etchingresist film at positions corresponding to lenslets while the glasssubstrate is held undamaged.

A process for fabricating a mother matrix by use of the glass mastermatrix of FIG. 1H will next be described with reference to FIGS. 3A to3E. A metallic material for the mold may be Ni or Ni alloy. In thefollowing description, Ni is used as a material for the mold.

[2] Fabrication of Mother Matrix

(a) Application and Drying of Parting Agent

As shown in FIG. 3A, a glass master matrix 30 is immersed in a fluoricparting agent 32 contained in a tank 34, thereby applying the partingagent 32 onto the surface of the glass master matrix 30 in the form of amonomolecular layer. The parting agent 32 facilitates the parting of theglass master matrix 30 in a later parting step in order to preventbreakage of the glass master matrix 30. The applied parting agent 32 isdried.

(b) Dropping of Resin

As shown in FIG. 3B, by use of a dispenser, a resin 36 is dropped ontothe glass master matrix 30 such that air is not caught in the droppedresin 36 in the form of bubbles.

The resin 36 to be used is a UV-during resin having the followingproperties. Cure shrinkage: not greater than 6%; viscosity: 100 to 2000cP (at 25° C.); hardness after curing: 1 to 5H; and bonding strength: 5kg/6 mm diameter (glass/glass, 100 μm thick).

In place of a UV-curing resin, a thermosetting resin or a two-partsystem resin may be used.

(c) Spreading of Resin and UV Curing

As shown in FIG. 3C, a glass substrate 38 is placed on the droppedUV-curing resin 36 so as to spread the resin 36. The glass substrate 38has good flatness and has a thickness of at least 0.3 mm so as not todeform when a stress is generated therein during Ni plating, which willbe described later.

Specifically, the glass substrate 38 is lowered from above the resin 36.After the glass substrate 38 comes into contact with the resin 36,pressure is applied to the glass substrate 38 so as to spread the resin36. The pressure to be applied depends on the thickness of a portion ofthe spread resin 36 other than a lens pattern portion. When the portionis to have a thickness of 5 to 10 μm, the applied pressure is preferably50 to 100 kg/cm². In order to prevent air from being caught in the resin36 in the form of bubbles during spreading, the glass substrate 38 ispressed at a rate of not greater than 10 μm/sec.

In order to cure the resin 36, the thus-obtained sandwich body isirradiated with UV light having a wavelength of 300 to 400 nm and anenergy of 4000 mJ/cm².

(d) Parting

Next, as shown in FIG. 3D, a peripheral portion of the glass mastermatrix 30 is opened apart so that the glass master matrix 30 is partedfrom the resin 36 through introduction of air therebetween, therebyobtaining a mother matrix 40 as shown in FIG. 3E.

A process for fabricating an Ni mold by use of the thus-fabricatedmother matrix 40 will next be described with reference to FIGS. 4A to4C.

[3] Fabrication of Ni Mold

(a) Formation of Conductive Film

As shown in FIG. 4A, a conductive film 42 is formed on the resin 36 ofthe mother matrix 40. The conductive film 42 can be formed by, forexample, electroless Ni plating.

(b) Fabrication of Ni Mold

As shown in FIG. 4B, the conductive film 42 is plated with Ni. Thisplating is performed in the following manner. As shown in FIG. 5, anelectrolyte (Ni plating solution) 44 is heated to an appropriatetemperature and is held at the temperature. An Ni pellet to beelectrodeposited is connected to an anode side, while the mother matrix40, which is an object of electrodeposition (plating), is connected to acathode side. When current is applied, Ni on the anode side is dissolvedinto the electrolyte 44 and is deposited on the cathode side. As aresult, a Ni plating 46 is formed on the conductive film 42 of themother matrix 40. In order to maintain rigidity as a mold duringinjection molding, the thickness of the Ni plating 46 is rendered notless than 0.3 mm.

(c) Parting and Peripheral Machining

Next, as shown in FIG. 4C, the Ni plating 46 is parted from the mothermatrix 40. In order to prepare the Ni plating 46 for attachment to a dieset so as to be used as a mold for injection molding, the Ni plating 46undergoes peripheral machining, such as chamfering or beveling.

A process for fabricating the Ni mold is not limited to theabove-described process. The Ni mold may be fabricated in the followingmanner. A conductive film of Ni is formed by electroless plating on thesurface of the glass master matrix 30 on which concaves are formed. Theobtained glass master matrix 30 plated with Ni is used as a mothermatrix and undergoes the above-described steps (b) and (c), therebyfabricating the Ni mold through Ni plating.

A process for fabricating a lens plate by use of the thus-fabricated Nimold will next be described with reference to FIGS. 6A and 6B.

[4] Injection Molding

(a) Attachment of Molds

As shown in FIG. 6A, the two Ni molds fabricated by the above-describedprocess are attached to a die set (not shown) such that the patternedsurfaces thereof face each other. A mold 50 is set stationary, whereasother mold 52 is set movable. In this case, a tolerance for misalignment(including a rotational misalignment) between the facing patternedsurfaces is ±50 μm, and a tolerance for a gap between the two Ni moldsis ±50 μm. The position of the attached movable mold 52 is adjusted soas to satisfy the tolerances.

(b) Injection Molding

A molding resin 54 is injected into a gap formed between the two moldsattached to the die set. The molding resin 54 is an acrylic resin, andheat resistance thereof can be selected as appropriate. Resintemperature is set to about 250° C. (preferably not higher than 250° C.;at a resin temperature in excess of 250° C., the molding resin 54discolors). Mold temperature is set to about 80° C. (preferably nothigher than 100° C.; at a mold temperature in excess of 100° C., themold deforms).

Upon completion of mold injection in step (b), as shown in FIG. 6B, themolds are parted, and a molded lens plate 56 is taken out. In the caseof injection molding, the lens plate 56 is rarely molded as intended,but warps convexly to either side.

FIG. 7 is a plan view showing an example lens plate 56 fabricated byinjection molding. A lens pattern portion is not illustrated. The lensplate 56 assumes a rectangular shape measuring 140 mm×110 mm. Withinthis rectangular region, lenslets are arrayed. Each of the lenslets hasa diameter of about 600 μm, a height of about 74 μm, and a curvatureradius of about 647 μm. The thickness of the lens plate 56 is about 1.74mm, and the thickness of the lenslet (distance between the apexes ofopposite lenslets) is about 1.88 mm. A thin clipping portion 58 isprovided at 6 peripheral positions of the lens plate 56. Two engagementspigots 60 and two engagement sockets 62 for alignment use are providedat four corners on each side of the lens plate 56. The positionalaccuracy of the engagement spigots 60 and sockets 62 is ±100 μm. Theclipping portions 58 and the engagement spigots 60 and sockets 62 aresimultaneously molded during the injection molding of the lens plate 56.

In the above embodiment, the injection-molded lens plate 56 hashemispherical lenslets formed on both sides thereof. When a lens platehaving hemispherical lenslets formed on a single side thereof is to bemolded, one mold is replaced with a flat metallic plate which does nothave concaves formed therein. The flat metallic plate may be an Niplate, for example.

FIGS. 8A and 8B each show an array of hemispherical lenslets of a lensplate which has hemispherical lenslets formed on both sides thereof.FIG. 8A shows an array of hemispherical lenslets 65 in which opticalaxes 66 of the opposite hemispherical lenslets 65 are aligned in adirection perpendicular to a plane of the lens plate 64. FIG. 8B showsan array of the hemispherical lenslets 65 in which the optical axes 66of the opposite hemispherical lenslets 65 are aligned in an inclineddirection in relation to a plane of the lens plate 64.

Preferably, the lens plate 64 is coated with an antireflection film on aside where the hemispherical lenslets 65 are formed. The antireflectionfilm may be an SiO₂ film formed by, for example, sputtering, vapordeposition, or immersion.

Preferably, the lens plate 64 is coated with an anti-water absorptionfilm on a side where the hemispherical lenslets 65 are formed. Theanti-water absorption film may be a TiO₂ or ITO film formed by, forexample, sputtering, vapor deposition, or immersion.

The antireflection film and the anti-water absorption film must have arefractive index smaller than that of a material for the lens plate 64.

A process for assembling two lens plates into a lens array will next bedescribed.

[5] Assembly

A procedure for stacking lens plates will be described. As mentionedpreviously, an injection-molded lens plate involves molding shrinkage.

In order to correct a warp of each lens plate and assemble an erectimage, unity magnification, resin lens array which is free of imagedistortion, two lens plates 66 and 67 are stacked such that convexlywarped sides thereof face each other or face in the same direction asshown in FIGS. 9A and 9B. In the case where the convexly warped sidesface in the same direction, stacking must be such that the convexlywarped side of the lens plate whose warp is greater than that of theother lens plate faces the concavely warped side of the other lensplate. This arrangement prevents formation of a gap between the stackedlens plates.

The thus-stacked lens plates 66 and 67 are secured by clipping atperipheral positions thereof, which will be described later. Thus, thewarps of the lens plates 66 and 67 are corrected.

In order to assemble lens plates having molding shrinkage into an erectimage, unity magnification, resin lens array free of image distortion,the following must be considered. As shown in FIG. 10, molding shrinkageof a lens plate is distributed substantially symmetrically with respectto a direction (represented by arrow C) of resin injection from a gate(not shown). In other words, in FIG. 10, when letter D represents acenter axis of a passage of an injected resin, molding shrinkage isdistributed substantially symmetrically with respect to the axis D(represented by the dashed line). FIG. 10 shows the direction andmagnitude of molding shrinkage by arrows.

Since molded lens plates exhibit a substantially similar magnitude ofmolding shrinkage, the optical axes of stacked hemispherical lensletscan be aligned by stacking two lens plates in appropriate orientation.

In FIG. 6B, lens plates molded by use of the same molds are stacked suchthat gate positions thereof are located on the same side, i.e.,directions of resin injection thereof are aligned. Such a way ofstacking nullifies the influence of molding shrinkage, so that a unitymagnification, erect image can be obtained. Other way of stackingsuffers the influence of molding shrinkage. Specifically, in the twostacked lens plates, the optical axes of stacked hemispherical lensletsare not aligned; as a result, an image is distorted, resulting in afailure to obtain a unity magnification, erect image.

In order to implement an erect image, unity magnification lens array bymeans of two stacked lens plates, the optical axes of at least threestacked hemispherical lenslets must be aligned. Accordingly, one lensplate has hemispherical lenslets formed on both sides thereof, whereasthe other lens plate has hemispherical lenslets formed on at least asingle side. In order to align the optical axes of at least threestacked hemispherical lenslets, the two lens plates must be stacked inan aligned manner. To achieve alignment between the two stacked lensplates, the two engagement spigots 60 and two engagement sockets 62 foralignment use are provided at four corners on each side of each lensplate. Through engagement of the spigots 60 and the correspondingsockets 62, the two lens plates can be stacked in an aligned manner.

As shown in FIG. 11, the diameter of the spigot 60 and the diameter ofthe socket 62 may be selected such that, when the spigot 60 and thesocket 62 are engaged, a clearance x is left therebetween, thusperforming rough alignment. Subsequently, fine alignment may beperformed through adjustment within the clearance x so that the opticalaxes of the two lens plates are aligned. In this case, the clearance xis selected such that adjustment can be completed within a rangecorresponding to a single lenslet.

FIG. 12A shows the two lens plates 56 and 57 to be stacked. The lensplates 56 and 57 each have protuberances 76 provided in a region otherthan a region of hemispherical lenslets. The height of the protuberances76 is substantially equal to that of the hemispherical lenslets. Theprotuberances 76 are adapted to adjust the distance between the apexesof facing hemispherical lenslets. When the distance between the apexesof facing hemispherical lenslets becomes equal to or greater thanone-tenth of a lenslet diameter, an image is deteriorated. Therefore,adjustment of the distance between the apexes of facing lenslets is veryimportant.

After the lens plates 56 and 57 are stacked and aligned throughengagement of the spigots 60 and the sockets 62, clips 80 of an ironmaterial are fitted to the clipping portions 58 as shown in FIG. 12B soas to secure the lens plates 56 and 57 as shown in FIG. 12C. Since theheight of the protuberances 76 is substantially equal to that ofhemispherical lenslets, the apexes of hemispherical lenslets contacteach other.

Next will be described an example in which the two lens plates 56 and 57are stacked while a colored spacer is interposed therebetween.

As shown in FIG. 13A, the two lens plates 56 and 57 are stacked while acolored spacer 70 of metal or resin is interposed therebetween openings72 corresponding to hemispherical lenslets and openings 74 correspondingto the engagement spigots 60 are formed in the colored spacer 70. Thecolored spacer 72 is intended: (1) to shut off stray light which wouldotherwise pass through a region other than hemispherical lenslets; (2)to hold the distance between the lens plates 56 and 57 to thereby adjustthe distance between the apexes of facing lenslets; (3) to contribute tothe correction of a warp of the lens plates 56 and 57; and (4) to alignthe two lens plates 56 and 57. The thickness of the colored spacer 70 issubstantially equal to a value two times the hemispherical-lensletheight. The colored spacer 70 is colored black and mat.

The two lens plates 56 and 57 are aligned through engagement of thespigots 60 and the sockets 62 while the colored spacer 70 is interposedtherebetween. Next, the clips 80 are fitted to the correspondingclipping portions 58 as shown in FIG. 13B, thereby securing the lensplates 56 and 57 as shown in FIG. 13C. As a result, the distance betweenthe apexes of facing hemispherical lenslets of the lens plates 56 and 57is held constant.

Further, in the case where the thickness of the colored spacer issmaller than a value two times the height of a hemispherical lenslet,clipping two lens plates at peripheral edges involves the followingproblem. Since the total height of facing hemispherical lenslets of thetwo lens plates becomes greater than the gap between facing peripheralportions of the two lens plates stacked with the colored spacerinterposed therebetween, the two lens plates warp while the peripheraledges of the hemispherical-lenslet regions thereof serve as fulcrums. Asa result, the distance between facing hemispherical lenslets fails to beheld constant in central portions of the hemispherical-lenslet regionsof the two lens plates. Therefore, it is important to provideprotuberances at peripheral portions of the lens plates so that the gapbetween facing peripheral portions of the two lens plates stacked withthe colored spacer interposed therebetween assumes a value about twotimes the height of a hemispherical lenslet.

Since a coefficient of thermal expansion differs between the resin lensplates and the colored spacer interposed between the resin lens plates,a resultant stress is generated. Such stress causes misalignment betweenthe optical axes of stacked hemispherical lenslets and is thusundesirable. Therefore, a coefficient of thermal expansion of thecolored spacer must be selected so as to meet the following expression.

α2≦α1+0.5×P/(T×L)

where α1 is a coefficient of thermal expansion of a material for thelens plate; α2 is a coefficient of thermal expansion of a materiel forthe colored spacer; L is a longitudinal length of the lenslet region ofthe lens plate; P is a minimum pitch of lenslets; T is a workingtemperature range; and a coefficient of 0.5 is intended to align theoptical axis of a hemispherical lenslet with the center of an openingformed in the colored spacer at one longitudinal end of the lensletregion and to render an offset of the optical axis of a hemisphericallenslet from the center of an opening formed in the colored spacer notgreater than half pitch at the other longitudinal end of the lensletregion.

For example, in the case of coefficient al of thermal expansion of thelens plate=7×10⁻⁵ (acrylic), longitudinal length L=120 mm, lenslet pitchP=0.6 mm, and working temperature range T=30° C., a material for thecolored spacer may be selected such that coefficient α2 of thermalexpansion thereof conforms to the expression “α2≦1.53×10⁻⁴.” Such amaterial is, for example, stainless steel (α1≦1.28×10⁻⁶).

In the above embodiment, the lens plates are secured only by clipping.However, an adhesive may be additionally used. In this case, theadhesive (solvent acceptable) is introduced into the engagement sockets.The engagement sockets and the corresponding engagement spigots areengaged to align two lens plates. Then, the engaged portions of the lensplates are pressed so as to temporarily secure the lens plates. Theclips 80 are fitted to the clipping portions 18, thereby securing thetwo lens plates. When clipping and bonding are used cooperatively forsecuring the two lens plates, the lens plates and the colored spacermust not be bonded.

FIG. 14 shows a spatial transmission of an image lying in an objectplane onto an image plane through an erect image, unity magnification,resin lens array 82 fabricated according to the present invention.Letter L represents a spatial distance.

FIG. 15 shows MTF (Modulation Transfer Function), an optical property,of the erect image, unity magnification, resin lens array as measured byuse of a rectangular wave having a spatial frequency of 1 Lp/mm whilespatial distance L is varied from 10 mm to 100 mm in units of 10 mm. AnMTF of 20% is a limit sensible by human. As seen from FIG. 15, an erectimage, unity magnification, resin lens array having a lenslet diameterof 0.3 mm to 1.0 mm and a spatial distance of 20 mm to 100 mm exhibits agood MTF value. Therefore, the erect image, unity magnification, resinlens array of the present invention provides an image of good qualitylying in an image plane.

The embodiments of the present invention have been described above.However, it will be apparent to those skilled in the art that theinvention is not limited thereto, but may be varied or modified withoutdeparting from the scope of the invention.

Industrial Applicability

According to the present invention, two lens plates are fabricated byinjection molding and are assembled into an erect image, unitymagnification, resin lens array, whereby erect image, unitymagnification, resin lens arrays of uniform quality can be readilymanufactured at low cost.

What is claimed is:
 1. A method for manufacturing a lens plate which has hemispherical lenslets arrayed in a regular pattern on at least one sides thereof, comprising the steps of: applying a parting agent onto a surface of a master matrix of glass on which concaves are formed, followed by drying; dropping resin onto the surface of the master matrix on which concaves are formed; spreading the dropped resin by pressing a substrate having parallel, flat surfaces against the dropped resin; curing the spread resin; parting the master matrix; forming a conductive film on the cured resin; depositing metal on the conductive film to a predetermined thickness by plating; parting the resultant metal plating from the cured resin to thereby obtain a mold having concaves formed therein; attaching the mold having concaves formed therein and a flat-surface mold onto a die set such that the concaves and the flat surface face each other; establishing a predetermined gap between the facing molds and injecting resin into the gap; and opening the molds apart to remove the lens plate.
 2. A method for manufacturing a lens plate, which has hemispherical lenslets arrayed in a regular pattern on at least one sides thereof, comprising the steps of: forming a conductive film on a surface of a master matrix of glass on which concaves are formed; depositing metal on the conductive film to a predetermined thickness by plating; parting the resultant metal plating from the master matrix to thereby obtain a mother matrix; forming a parting layer on the mother matrix and depositing metal on the parting layer to a predetermined thickness by plating; parting the resultant metal plating from the mother matrix to thereby obtain a mold having concaves formed therein; attaching the mold having concaves formed therein and a flat-surface mold onto a die set such that the concaves and the flat surface face each other; establishing a predetermined gap between the facing molds and injecting resin into the gap; and opening the molds apart to remove the lens plate.
 3. A method for manufacturing a lens plate which has hemispherical lenslets arrayed in a regular pattern on both sides thereof, comprising the steps of: a) applying a parting agent onto a surface of a master matrix of class on which concaves are formed, followed by drying; b) dropping resin onto the surface of the master matrix on which concaves are formed; c) spreading the dropped resin by pressing a glass substrate having parallel, flat surfaces against the dropped resin; d) curing the spread resin; e) parting the master matrix; f) forming a conductive film on the cured resin; g) depositing metal on the conductive film to a predetermined thickness by plating; h) parting the resultant metal plating from the cured resin to thereby obtain a first mold having concaves formed therein; i) repeating steps g) and h) to thereby obtain a second mold having concaves formed therein j) attaching the first and second molds, each having concaves formed therein, onto a die set such that surfaces having the concaves formed therein face each other; k) establishing a predetermined gap between the facing molds and injecting resin into the gap; and l) opening the molds apart to remove the lens plate.
 4. A method for manufacturing a lens plate, which has hemispherical lenslets arrayed in a regular pattern on both sides thereof, comprising the steps of: a) forming a conductive film on a surface of a master matrix of glass on which concaves are formed; b) depositing metal on the conductive film to a predetermined thickness by plating; c) parting the resultant metal plating from the master matrix to thereby obtain a mother matrix; d) forming a parting layer on the mother matrix and depositing metal on the parting layer to a predetermined thickness by plating; e) parting the resultant metal plating form the mother matrix to thereby obtain a first mold having concaves formed therein; f) repeating steps d) and e) to thereby obtain a second mold having concaves formed therein; attaching the first and second molds, each having concaves formed therein, onto a die set such that surfaces having the concaves formed therein face each other; establishing a predetermined gap between the facing molds and injecting resin into the gap; and opening the molds apart to remove the lens plate.
 5. A method for manufacturing a lens plate according to any of claims 1-4, wherein the master matrix is manufactured by the steps of; preparing a glass substrate having substantially parallel, flat surfaces; forming an etching resist film on the glass substrate; forming fine openings corresponding to the hemispherical lenslets in the etching resist film in a regularly arrayed pattern; isotropically etching the glass substrate while the etching resist film is used as a mask, thereby forming concaves in the glass substrate under the corresponding fine openings; removing the etching resist film; and further isotropically etching the glass substrate so that the concaves grow and assume a profile corresponding to that of the hemispherical lenslet.
 6. A method for manufacturing a lens plate according to claim 5, wherein, in the step for forming the fine openings in the etching resist film in a regularly arrayed pattern, portions of the etching resist film which correspond to the fine lenslets are irradiated with an electromagnetic wave so as to be heated and evaporated.
 7. A method for manufacturing a lens plate according to claim 6, wherein an etching resist film is formed on a back surface of the glass substrate before the second isotropic etching is carried out.
 8. A method for manufacturing a lens plate according to any of claim 1-4 wherein the master matrix is manufactured by the steps of: preparing a glass substrate having substantially parallel, flat surfaces; forming a metallic film on the glass substrate; applying a photoresist onto the metallic film; pattering the photoresist; etching the metallic film while the patterned photoresist is used as a mask, thereby forming fine openings corresponding to the hemispherical lenslets in the metallic film in a regularly arrayed pattern; removing the photoresist; isotropically etching the glass substrate while the metallic film is used as a mask, thereby forming concaves in the glass substrate under the corresponding fine openings; removing the metallic film; and further isotropically etching the glass substrate so that the concaves grow and assume a profile corresponding to that of the hemispherical lenslet.
 9. A method for manufacturing a lens plate according to claim 8, wherein an etching resist film is formed on a back surface of the glass substrate before the second isotropic etching is carried out.
 10. A method for manufacturing a lens plate according to any of claims 1-4, wherein the master matrix is manufactured by the step of: preparing a glass substrate having substantially parallel, flat surfaces; forming a metallic film on the glass substrate; applying a photoresist onto the metallic film; patterning the photoresist; etching the metallic film while the patterned photoresist is used as a mask, thereby forming fine openings corresponding to the hemispherical lenslets in the metallic film in a regularly arrayed pattern; isotropically etching the glass substrate while the metallic film coated with the photoresist is used as a mask, thereby forming concaves in the glass substrate under the corresponding fine openings; removing the photoresist and the metallic film; and further isotropically etching the glass substrate so that the concaves grow and assume a profile corresponding to that of the hemispherical lenslet.
 11. A method for manufacturing a lens plate according to claim 10, wherein an etching resist film is formed on a back surface of the glass substrate before the second isotropic etching is carried out.
 12. A method for manufacturing a lens plate according to any of claim 1-4, wherein the master matrix is manufactured by the steps of: preparing a glass substrate having substantially parallel, flat surfaces; forming a metallic film on the glass substrate; applying a first photoresist onto the metallic film; patterning the first photoresist; etching the metallic film while the patterned first photoresist is used as a mask, thereby forming fine openings corresponding to the hemispherical lenslets in the metallic film in a regularly arrayed pattern; removing the first photoresist; applying a second photoresist; exposing the second photoresist to light emitted from behind the glass substrate, through the fine openings formed in the metallic film; removing exposed portions of the second photoresist by development; isotropically etching the glass substrate while the metallic film coated with the second photoresist is used as a mask, thereby forming concaves in the glass substrate under the corresponding fine openings; removing the second photoresist and the metallic film; and further isotropically etching the glass substrate so that the concaves grow and assume a profile corresponding to that of the hemispherical lenslet.
 13. A method for manufacturing a lens plate according to claim 12, wherein an etching resist film is formed on a back surface of the glass substrate before the second isotropic etching is carried out.
 14. A method for manufacturing a lens plate according to any of claims 1-4, wherein the master matrix is manufactured by the steps of: preparing a glass substrate having substantially parallel, flat surfaces; forming a metallic film on the glass substrate; applying a first photoresist onto the metallic film; patterning the first photoresist; etching the metallic film while the patterned first photoresist is used as a mask, thereby forming fine openings corresponding to the hemispherical lenslets in the metallic film in a regularly arrayed pattern; applying a second photoresist; exposing the second photoresist to light emitted from behind the glass substrate, through the fine openings formed in the metallic film; removing exposed portions of the second photoresist by development; isotropically etching the glass substrate while the metallic film coated with the first photoresist and the second photoresist is used as a mask, thereby forming concaves in the glass substrate under the corresponding fine openings; removing the first photoresist, the second photoresist, and the metallic film; and further isotropically etching the glass substrate so that the concaves grow and assume a profile corresponding to that of the hemispherical lenslet.
 15. A method for manufacturing a lens plate according to claim 14, wherein an etching resist film is formed on a back surface of the glass substrate before the second isotropic etching is carried out. 